In many medical procedures, various physiological conditions present within a body cavity need to be monitored. These physiological conditions are typically physical in nature—such as pressure, temperature, rate-of-fluid flow, and provide the physician or medical technician with critical information as to the status of a patient's condition.
One device that is widely used to monitor conditions is the blood pressure sensor. A blood pressure sensor senses the magnitude of a patient's blood pressure, and converts it into a representative electrical signal that is transmitted to the exterior of the patient.
For most applications it is required that the sensor is electrically energized. Some means of signal and energy transmission is thus required, and most commonly extremely thin electrical cables, sometimes called microcables, are provided inside a guide wire, which itself is provided in the form of a tube, which often has an outer diameter in the order of 0.35 mm, and oftentimes is made of steel.
In order to increase the bending strength of the tubular guide wire, a core wire is positioned inside the tube. The core wire also helps to improve “pushability” and “torquability” of the guide wire. The mentioned electrical cables are e.g. positioned in the space between the inner lumen wall and the core wire.
Sensor and guide wire assemblies in which a sensor is mounted at the distal end of a guide wire are known. In U.S. Pat. No. Re. 35,648, which is assigned to the present assignee, an example of such a sensor and guide wire assembly is disclosed, where a sensor guide comprises a sensor element, an electronic unit, a signal transmitting cable connecting the sensor element to the electronic unit, a flexible tube having the cable and the sensor element disposed therein, a solid metal wire, and a coil attached to the distal end of the solid wire. The sensor element comprises a pressure sensitive device, typically a membrane, with piezoresistive elements connected in a Wheatstone bridge-type of arrangement mounted thereon.
As is disclosed in, for example, U.S. Pat. No. 6,167,763, which also is assigned to the present assignee, the sensor element can be arranged inside a short tube (usually referred to as a sleeve or jacket), which protects the sensor element and comprises an aperture through which the pressure sensitive device is in contact with the ambient medium. The U.S. Pat. No. 6,167,763 further illustrates that a first coil may be attached to the distal end of the jacket and that a similar second coil may be attached to the proximal end of the jacket. The solid metal wire—which, as also mentioned above, in the art usually is referred to as the core wire—extends through the interior of the jacket and may be provided with an enlarged diameter portion adapted for mounting of the sensor element.
U.S. Pat. No. 7,222,539 discloses a jacket, wherein a sensor element and a core wire are provided in separate compartments. Another example of a sensor guide wire comprising a sensor enclosed by a sensor housing is disclosed in WO 2006/037082 A2.
In WO 03094693 A2, a pressure-measuring apparatus is disclosed, the pressure-measuring apparatus comprises a sensor transducer adapted to be incorporated in a catheter.
DE 2420610 A1, discloses a sensor for measuring pressure, the sensor is adapted to be incorporated in a catheter. The sensor is enclosed by a protecting tube.
U.S. Pat. No. 6,019,728 discloses a catheter including a catheter tube to be inserted into a body. A plurality of sensing portions are arranged in the catheter tube. Two pressure communication holes are provided in the wall of the catheter tube to communicate the ambient pressure of the tube into the interior of the tube.
In US 2007088220 A1 an implantable medical device including a physiological sensor is disclosed. The sensor is embedded in a mesh structure of a stent-like structure.
In US 20050187487 A1 and US 20060211946 A1, further examples of catheters provided with sensors are disclosed.
U.S. Pat. No. 6,162,182 discloses a cannula usable to remove blood from a patient during surgery.
Generally, a sensor and guide wire assembly comprises a sensor element in the form of an elongated, essentially rectangular chip with a pressure sensitive member in the form of a membrane provided thereon. The sensor chip is arranged inside a jacket, which besides the sensor chip also accommodates a portion of a core wire and at least one electrical lead connected to the sensor element. A first coil may be attached to the distal end of the jacket, and optionally a second coil may be attached to the proximal end of the jacket. The first and second coils may be attached to the respective end of the jacket, e.g. by gluing, or alternatively soldering.
Although sensor and guide wire assemblies comprising a jacket designed according to the techniques presented by the present assignee in practise have proven to work very well, there are continuously ongoing efforts to improve the performance and functionality of the sensor and guide wire assemblies.
According to the prior art, the jacket is provided with an aperture or window, through which the pressure sensitive part (typically a membrane) of the sensor element is in communication with a surrounding medium, e.g. blood. Now, it has—for the first time—been recognized that the dimensions of the aperture, the sensor element and the interior of the jacket in combination with the particular mounting arrangement of the sensor element are such that air present within the jacket and/or adhering to the surface of the jacket or sensor element has a tendency to be entrapped within the jacket and/or forming an air bubble covering the aperture in the jacket. In other words, the ambient fluid (e.g. blood) does not wet the sensor element and the membrane completely, which affects the signal quality of the device.
An object of the present invention is therefore to provide a sensor and guide wire assembly comprising an improved jacket, with which the above-mentioned wetting problem is eliminated or at least minimized.